Growing commitments threaten upper Verde River flow

Escalating groundwater commitments threaten severe reduction if not complete loss of perennial flow in the upper 24 miles of the Verde River.

The implications include severe damage to habitat along this reach of the river, substantial reduction of surface water along the length of the river, and a marked degradation of the quality of life that makes northern Arizona so attractive.

Although Arizona law does not recognize their linkage, the one between groundwater and surface is intimate. Water use anywhere in the watershed affects populations and habitat downstream. Accordingly, long-term sustainability of our limited water resources will require regional management of the watershed.

All stakeholders must have a voice. It will require compromise as well as new legislation that facilitates water-resource management in the best interest of all. Accordingly, the North Central Arizona Regional Watershed Consortium is sponsoring a workshop on Saturday at the Davis Learning Center, Embry-Riddle Aeronautical University.

It will be a grass-roots effort to form a regional water-management partnership to ensure long-term sustainability and quality of life in the Verde River basin.

All groundwater that enters an aquifer ultimately discharges from it, and, over the long term, recharge to an aquifer or groundwater system equals discharge from it. The introduction of pumping by man removes water that otherwise would have discharged naturally from an aquifer, so that the amount of water withdrawn by wells eventually results in an equal reduction in discharge. That discharge of groundwater to streams from springs and seeps – also known as base-flow – maintains perennial flow in our rivers.

We preserve base-flow only if recharge to the aquifer exceeds with-drawals.

The Verde River originates from the discharge of groundwater beginning near the mouth of Granite Creek, and most of the discharge that supplies base-flow in the upper 24 miles of the Verde River originates within the next two river miles. About 20 percent of this water is from the Little Chino sub-basin. Most if not all of the remaining upper Verde River base-flow originates from groundwater in the Big Chino sub-basin.

Either achievement of safe yield or continuing groundwater overdrafts in the Prescott Active Management Area eventually will reduce the contribution from the Little Chino sub-basin to zero.

Further, existing or likely groundwater commitments in the Big Chino sub-basin already equal or exceed the current (pre-drought) average upper Verde River base-flow of 18,000 acre-feet per year. The City of Prescott, in combination with the Town of Prescott Valley, now has committed to importing approximately 8,700 acre-feet a year of groundwater from the Big Chino sub-basin. Yavapai County Water Advisory Committee data indicate that it's legal to import an estimated additional 11,000 to 12,600 acre-feet a year of groundwater representing retired irrigation rights in the Prescott Active Management Area. No doubt, pressure will be intense to acquire that legally available retired irrigation-right water to support continuing development in the AMA. These commitments alone exceed the total base-flow in the uppermost Verde River.

Development in the Big Chino sub-basin can only deepen the projected groundwater deficit. An ever-growing community in the vicinity of Paulden relies on Big Chino groundwater. Subdivisions along the margins of Williamson Valley exist off groundwater from the Big Chino sub-basin.

A planned-area development of 25,000 homes in the central part of Big Chino Valley that would have drawn Big Chino groundwater didn't happen, but it represents the kind of evolution we should expect. If not planned area developments, then development via endless wildcat lot splits is in the cards.

The Verde River basin involves parts of three counties – Coconino, Maricopa and Yavapai; many municipalities; four national forests – Coconino, Kaibab, Prescott and Tonto; tribal lands; state trust lands; federal and state park lands; and private unincorporated lands.

Representatives of all who manage these lands and those who use them have a critical vested role in judicious management of the water that supports them and their use.